Grease containing silica gel treated



Patented Aug. 7, 1951 UNITE GREASE CONTAINING SILICA GEL TREATED WITH A POLYHYDRIC ALCOHOL Charles N. Kimberlin, Jr., and Augustus B. Small, Baton Rouge, La., assignors to Standard Oil Development Company, a corporation of Delaware N Drawing. Application July 24, 1947, Serial No. 763,439

9 Claims. (01. 252-28) 1 This invention relates to solvent resistant greases and lubricating compositions and more particularly to normally solid or grease-like compositions which are suitable for lubricating bear- Prior to our present invention, there has been considerable difl'iculty in providing proper lubrication for mechanical elements operating in the presence of certain chemicals. Ordinary lu bricating compositions of hydrocarbon oil base are highly satisfactory for lubricating many types of mechanisms but in the presence of liquid hydrocarbons and various other chemicals they are readily dissolved, washed out, or otherwise rendered inefficient or ineffective. In' certain types of apparatus, such as mixing vats, and in chemical reaction vessels containing movable mechanical parts, such as stirrers, and the like, it has been very diflicult to provide suitable lubrication. This is particularly true in certain types of apparatus operating at unusual temperatures. For

example, mechanical processing equipment for polymerizing hydrocarbons, such as isobutylene, isoprene, etc., at very low temperatures has presented a particular problem. Apparatus of this character is frequently operated at temperatures far below freezing and as low as l50 F. or lower. The hydrocarbon reactants are commonly associated with other solvents, such as methyl chloride and the like which also tend to dissolve out and destroy ordinary lubricants. In the past, lithium soap base greases have been used to some extent in this type of apparatus but have not been very satisfactory becaus the hydrocarbon oil constituents are leached or dissolved out of the lubricant.

Various types of chemical laboratory equipment and chemical plant equipment involving ground glass joints, stopcocks, and the like, require lubrication and a lubricant must be provided which will not be attacked chemically and will not be dissolved and carried away by the chemicals which are being used or processed. In many instances ordinary lubricating oils and greases of mineral oil base are not satisfactory for these uses.

It is, therefore, an object of our invention to compound a suitable lubricant which will be useful with hydrocarbons and other chemicals without being dissolved thereby and without being subject to undesirable chemical reaction with accompanying formation of materials which are deleterious to the surfaces and materials in the system lubricated. It is a further object to com- 2 pound a grease type lubricant which will retain its lubricating qualities at extreme temperatures and particularly at extremely low temperatures. Other and further objects will become apparent as this description proceeds.

We have found that when the water of an inorganic hydrogel or of other inorganic gelatinous precipitates is replaced by a liquid having lubricating properties but suitably resistant to solution or chemical reaction and properly milled a composition product having an excellent greaselike structure may be produced. The liquid chosen to replace the water preferablyhas a viscosity at least as high as water and preferably also a lower volatility. For appropriate purposes mineral base lubricating oil may be used as the liquid, replacement of the water requiring, however, that a mutual solvent be employed. The liquid selected, however, must not react materially with the gel and it must, of course, have lubricating properties.

The inorganic hydrogel or other gelatinous precipitate such as silica, alumina, stannia, etc., is treated in an appropriate manner as set forth hereinafter to replace the water by the lubricating liquid and is then subjected to milling. Milling is conducted in a manner which will thoroughly crush the gel and subject it to high shearing forces. The consistency of the finished product is determined by the proportion of the liquid to solid matter which is present. This proportion will normally be chosenso as to provide from 5% to 20% by weight of the solid matter, calculated on a water-free basis, in the finished product.

We have further found that by proper selection the liquid matter and the inorganic hydrogel or gelatinous precipitate may be chosen so as to provide proper resistance to a particular solvent or reagent in the presence of which the lubricant must be used. A lubricating grease or greaselike material produced from a liquid so chosen, we have found, will also be likewise resistant to attack by that particular solvent or reagent and the inorganic gel structure provides a suitable grease-like structure or body for th lubricant.

For example, if a grease which is resistant to to the solvent action of a hydrocarbon or chlorinated hydrocarbon solvent is desired, we have found that a combination of gelatinous silica or alumina with glycerol or a glycol proves satisfactory. 'I'horia, ferria, and other inorganic gelatinous materials also may be used as the starting material. Silica and alumina are generally preferred because of their low cost, common availability, color, stability, and ease of converting to handling anhydrous HCl gas.

3 the gelatinous form. On the other hand, if resistance to the chemical action of sulfuric acid or of liquid chlorine or bromine is desired, a combination of gelatinous silica with sulfuric acid as the liquid media may be chosen. Sulfuric acid has previously been used in the ordinary liquid form in apparatus for compressing and otherwise The grease just described has analogous applications n com centrated sulfuric acid forms an eflective combination with silica hydrogel when the water of the gel is replaced thereby.

The gelatinous substances contemplated by our the precipitate may be used. The liquid materials which are chosen to replace the normal water of gelation will in general includes such substances as glycerol, the glycols, especially ethylene or polyethylene glycol, and the corresponding propylene compounds, as well as higher glycols and other similar oxygenated or polar compounds such as esters of phosphoric acid or silicic acids, e. g. cresyl phosphate, cresyl orthosilicate, and the like. The esters of sugar alcohols such as sorbitan mono-laurate or polyethylene oxide derivatives thereof, and related derivatives may be used. Certain nitro compounds such as nitrobenzene may be employed and various amines and amine alcohols, e. g. triethanol amine may be used.

For resistanceto chemical attack, as distinguished from resistance to solvent action, various liquid materials may be chosen, such as sulfuric acid, phosphoric acid, silicone polymer oils, and the like. Sulfuric acid and phosphoric acid have been used in the past to lubricate glass joints, stop cocks, and the like, and greases may be prepared according to the present invention for related uses. In appropriate cases, as suggested above, hydrocarbon oils may be used to replace the water of the normal gel where the chemicals or other reagents present are not of a character to dissolve or react unfavorably with hydrocarbons.

It will be understood that greases prepared according to our invention are quite distinct in their character from the normal, soap base grease lubricants which are so widely used for lubricating purposes. They are nevertheless analogous and similar in many respects in their texture and other physical characteristics and it is within the scope of our invention to include in 'the lubricating composition such usual additives as antioxidants, corrosion inhibitors, extreme pressure agents, and the like, so long as they are compatible and useful with the liquid material being used. It is also within the scope of ourinvention to include such materials as the metallic soaps which normally might not be solvent resistant. Soaps may be used to replace part of the gel. In general they may comprise not more than 5% by weight of'the total composition. Thus a grease may be prepared using a combination of silica gel and zinc stearate as thickening tions formulated according to our invention may be prepared by several general methods. Thus in many cases the replacement of water in the gel may be accomplished by soaking the gelatinous material in a suflicient quantity of the desired liquid which is to replace the water, provided such liquid is miscible with water. However, if the liquid is immiscible with water, the water can first be replaced by a mutual solvent and the desired liquid then incorporated in the same general manner. After replacement of the water, and of the mutual solvent where such is employed, the product can be milled to develop grease structure. In general milling during manufacture is preferred but in some cases the use to which the grease is subjected will accomplish adequate milling.

' Another method for replacing the water in the gelatinous material is to mill the gelatinous material with the desired liquid in heated equipment operated at a temperature suflicient to evaporate the waterduring the milhng and con structed so as to permit the water to escape, for example, in the form of steam. A steam heated rubber mill or analogous equipment may be used for this purpose and in fact has been found to be well suited for such uses.

If the liquid portion which is to replace the water is water soluble, it may be incorporated in the composition in still another manner. It may beadded to a hydrosol or colloidal solution of the gelatinous material to give a homogeneous mixture. Thereafter the water may be evaporated and the product milled as previously indicated.

Generally speaking, the replacing liquid will have a. higher boiling point than water and if it is to be used at very low temperatures it should obviously have a very low freezing point. Very low freezing points may also be obtained by using a mixture of suitable liquids. The invention may be further illustrated by several examples.

EXALIPLE I To a sulfuric acid solution having a specific gravity of 1.19 there was added an equal volume of sodium silicate (Nan-3.25 SiOz), in a solution having a specific gravity of 1.21. The resulting hydrogel which formed was washed with water until free of sulfate ions. The product remaining was a hydrogel consisting of silica and water. The hydrogel was then treated with successive portions of glycerin at a temperature of to 200 F. until the water was completely replaced. The temperature was raised above normal to hasten the diifusion of glycerin into and water out of the gel structure. The excess glycerin and water were then drained oil. The gel was next milled in 9. Simpson type mill for three hours with small additions of glycerine in order to obtain the desired grease-like consistency. The resulting product had an excellent grease struc ture and was entirely resistant to the action of hydrocarbons and similar solvents. Its composition was 6.4% silica and 93.6% glycerine. Due to its glycerine content it was somewhat hygroscopic in character but it was found that a moderate amount absorption of water did not seriously detract from its usefulness.

The lubricant of Example I was used to seal and lubricate ground glass joints and stopcocks in laboratory equipment employed in the distillation of various etroleum products. It was found that the lubricant was quite satisfactory,

leaks being successfully prevented, and no frozen joints were encountered. 1

The replacement of the water of.a hydrogel with another (water miscible) liquid can be illustrated as follows: If a sponge containing water is placed into a vessel containing alcohol the alco- EXAMPLE II to be 13.5% silica and 86.5% glycerin. Except for the difference in consistency it was useful for the same general type of purpose as in the case of Example I.

EXAMPLE m A sample of silica hydrogel of the type described above in connection with Example I was worked on a steam heated rubber mill with ethyl ene glycol. During working the temperature was raised to remove the water by evaporation. 'Iwo other silica-ethylene glycol samples weretprepared in the same manner except that heating was discontinued before the water was completely removed. This was done for the purpose of producing a low temperature grease for use in contact with liquefied methyl chloride and liquefied ethylene ethane mixture in a butyl rubber reactor. It was found that the water has the effect of lowering the useful temperature range of greases prepared in this manner. 1

The three greases prepared by the method of Example III were found to be unaffected by boiling methyl chloride and bythe'boiling ethylene ethane. mixture. TableI below gives the approximate compositions, and penetrations of the three greases prepared by the method of Example III. The penetration numbers were determined with a conventional grease penetrometer, the depth of penetration being measured for a 300 gram weight acting for 5 seconds. For the determinations made at l1 F. each sample was immersed in boiling methyl chloride. For the tests made at -142 F. the sample was immersed in each instance in a boiling mixture of ethylene and ethane such as is used in the commercial production of butyl rubber. The greases were fairly hard in consistency at -142 F. but those containing water and glycol gave excellent performance in a butyl rubber reactor.

Table I Composition, Wt. Per Cent Penetration, mm.

sioi 0211mm: H2O -11 F. 142F.

1o 90 o 125 22 9 57 34 so 9 s1 24 320 36 6 EXAMPLEIV Still another example ofgrease prepared according to our invention was made by taking a peptized alumina hydrosol of the Patrick type containing 5% alumina which was prepared by treating amalgamated aluminum with 0.5% acetic acid solution, as set forth in U. S. Patent No. 2,258,099. An amount of glycerin equal to onehalf the volume of the peptized hydrosol was added thereto. This resulted in a homogeneous mixture which was evaporated in an oven at a temperature of 260 F. to remove the water. The resulting product was a transparent rather hard greasy semi-solid. This material was worked on a rubber mill to give very stiff grease. It had the composition 11% A1203, 89% glycerin. It is noted that a given amount of alumina gives a stiffer grease than a like quantity of silica.

Further experiments with greases of the silica hydrogelethylene glycol type, prepared by the manner set forth in Example III above, reveal that such greases are particularly suitable for the lubrication of mechanical equipment operating at very low temperatures in the presence of liquid hydrocarbons. A grease of this type has been found to give very satisfactory lubrication in a butyl rubber plant and its use for such purposes is being increased. The fact that such a grease has been found satisfactory in such equipment indicates that it gives good performance in the presence of liquid methyl chloride, liquid isobutylene, liquid isoprene, and also liquid ethane-ethylene which is used as a refrigerant. The grease may be used in the presence of liquid hydrocarbons of higher boiling points and greater viscosity at temperatures ranging from as low as 150 F. to normal room temperatures. The silica gel glycol type grease has been found to flow better at the low temperatures of butyl rubber polymerization than the lithium soap base greases which were used in the past.

It will be understood that the liquid material which replace water in the gel will be chosen for its resistance to solvent action or to chemical reaction with the particular material which it must encounter in use. Thus, although we have specifically mentioned such materials as glycerin,

the various glycols, sulfuric acid, phosphoric acid,

silicone polymer oils and the like, as well as hydrocarbon oils, it will be apparent that other liquid materials chosen for their particular purposes may be used with success.

We claim:

1. A lubricating grease composition capable of resisting the solvent action of low boiling hydrocarbons, consisting essentially of an inorganic hydrogel, the water of which has beensubstantially replaced by a polyhydric alcohol selected from the group consisting of glycerol and the monomeric and polymeric ethylene and propylene glycols.

2. A lubricating grease composition resistant to the solvent action of low boiling hydrocarbons and consisting essentially of an inorganic hydrogel,

the water of which has been substantially replaced by glycerol.

3. A lubricating grease composition suitable for the lubricating of mechanical equipment in the presence of low boiling hydrocarbons, consisting essentially of silica hydrogel, the water of which has been substantially replaced by ethylene glycol.

4. A low boiling hydrocarbon solvent resisting grease composition consisting essentially of silica hydrogel, the water of which is replaced by i a,scs,ooo

glycerin, said composition being milled to a grease-like consistency. I

5. A solvent resisting grease composition comprising 6.4 to 13.5% byvweight of silica and 51% and alcohol vigorously while maintaining a temperature oi at least, 180F. and sufllciently high to evaporate the water substantiallycompletely.

a. Process according to claim 1 whereirisaid to 93.6% or liquid polyhydric alcohol selected 5' alcohol is glyceroL' 9. Process according to claim 7 wherein said from the group consisting of glycerol and ethylene glycol. Y

6. A solvent resistant lubricating grease composition consisting essentially of a silica hydrogel, the water of which has-been substantially replaced by ethylene glycol, said composition consisting of 5 to 20% silica, 50 to 95% of said ethylene glycol and 0 to 40% water.

'7. The process or preparing a low temperature lubricating grease resistant to the solvent action 'of "low boiling hydr'o'carbons'T'ivhich' comprises glycerol and ethylene glycol and milling said gel,

alcohol is ethylene glycol.

CHARLESN.

AUGUSTUS B. SMALL.

nmnncss cn'm The following references are of record in th illc oithis patentz' e UNITED era-ms Pam-rs Number 7 Name Date 3,233,635 Kistler Oct. 28. 1841' ,1 1 Ballard Jill. 13,

Bass Oct. 7, 1947 

1. A LUBRICATING GREASE COMPOSITION CAPABLE OF RESISTING THE SOLVENT ACTION OF LOW BOILING HYDROCARBONS, CONSISTING ESSENTIALLY OF AN INORGANIC HYDROGEL, THE WATER OF WHICH HAS BEEN SUBSTANTIALLY REPLACED BY A POLYHYDRIC ALCOHOL SELECTED FROM THE GROUP CONSISTING OF GLYCEROL AND THE MONOMERIC AND POLYMERIC ETHYLENE AND PROPYLENE GLYCOLS. 